Process for making a fluid processing module

ABSTRACT

A process for making a fluid processing module is provided wherein a plurality of filtration elements is alternated with a fluid porous layer to form a stack. The filtration elements comprise a membrane sheet having a thermoplastic element bonded to a portion of an edge of the membrane. An opening is provided either through the membrane or through the thermoplastic element. A portion of the thermoplastic element extends into the opening and can be sealed to an adjacent positioned thermoplastic element to seal the porous sheet positioned between adjacently positioned membranes from fluid communication with the opening. Sealing can be effected by extending a heating element through the opening of the stack to effect simultaneous sealing of a plurality of thermoplastic elements.

BACKGROUND OF THE INVENTION

This invention relates to a process for making a fluid processing modulesuch as a membrane filtration apparatus for effecting filtration of aliquid composition wherein a feed liquid is introduced into theapparatus and a filtrate stream and, optionally a retentate stream areremoved from the apparatus. More particularly, this invention relates toa process for making a fluid processing module such as membranefiltration apparatus that are formed by indirect heat sealing of apolymeric composition.

For convenience, this invention will be described in detail withreference to a filtration module. However, it is to be understood thatthe process of this invention is equally applicable for making otherfluid processing modules such as manifolds, heat exchangers, dialysers,desalters, degassers and the like. Prior to the present invention,liquids have been filtered within a plurality of filter modules that arestacked between manifolds or individually sealed to a manifold plate.Each module includes a one or more filter layers separated byappropriate spacer layers, such as screens, to permit liquid feed flowinto the apparatus as well as filtrate flow from the apparatus.Filtration within the module can be conducted as a tangential flowfiltration (TFF) process wherein incoming feed liquid is flowedtangentially over a membrane surface to form a retentate and a filtrate.Alternatively, filtration can be conducted as a dead end mode otherwiseidentified as normal flow filtration (NFF) wherein all incoming feedliquid is passed through a membrane filter with retention of solids andother debris on the membrane filter. In this latter mode only a filtrateis recovered.

At the present time, a filtrate stream is sealed from a feed streamwithin a membrane filtration apparatus by sealing techniques utilizingpotting adhesives such as epoxies, urethanes or silicones, solventbonding or direct heat sealing. In the case of a tangential flowfiltration apparatus, a filtrate stream is sealed from a feed stream anda retentate stream. Adhesives are undesirable since they have limitedchemical compatibility, are a source of significant extractable species,introduce process control difficulties, impose bond strengthlimitations, impose use temperature limitations and increase processcycle time. Direct heat sealing wherein a heating element contacts amaterial that flows to form a seal is undesirable since its use imposesa minimal limitation upon the thickness of the material being heatsealed. This results in a reduction of the number of layers that can bepresent in a given volume of the filtration module, thereby undesirablyreducing the filtration capacity of the module. In addition, direct heatsealing is undesirable because it requires multiple steps, imposesmaterial compatibility limitations, and typically utilizes a substrateto effect direct heat-sealing of filtration elements and can causemembrane damage. Solvent bonding is undesirable since solvents imposeenvironmental issues and process variability while potentially usefulpolymers are limited by their solvation characteristics.

U.S. Pat. No. 5,429,742 discloses a filter cartridge comprising athermoplastic frame into which are molded a plurality of filtrationmembranes. The thermoplastic frame is molded to provide fluid pathwaysthat assure incoming fluid to be filtered to be passed through amembrane prior to removing filtered fluid from the filter cartridge. Theframe is sufficiently thick so that fluid pathways to and from themembranes can be formed. Since adjacent membranes are separated byrelatively thick spacer members, membrane area per unit volume of thefilter cartridge is undesirably low.

Accordingly, it would be desirable to provide a method for making afluid processing module such as a multilayer filtration apparatus whichutilizes a plurality of filtration elements wherein the layers areappropriately sealed without the use of adhesive, solvent bonding ordirect heat sealing. In addition, it would be desirable to provide aprocess for making a fluid processing module tangential flow containinga large number of layers such as filtration layers per volume offiltration apparatus which can be formed into a stack and which can beappropriately sealed to define liquid flow paths within the stack. Sucha filtration apparatus would provide a high filtration capacity andwould permit multiple uses of the apparatus.

SUMMARY OF THE INVENTION

The present invention provides a method for forming a fluid processingmodule such as a filtration apparatus formed of filtration elementswhich are sealed with a thermoplastic polymeric composition in a mannerwhich promotes sealing to a polymeric porous membrane while avoidingthermal or mechanical degradation of the membrane. Selective sealing ofthe porous polymeric membrane is effected in a two step process whereinat least one end of each membrane is sealed with a thermoplasticpolymeric composition to secure the thermoplastic polymeric compositionto the membrane. Selected layers of thermoplastic polymeric compositionson adjacently positioned membranes then are sealed to each other inorder to define fluid flow paths through the stack of alternatelypositioned membranes and spacer layers. The defined fluid flow pathsassure that fluid to be filtered passes through a membrane prior tobeing removed from the filtration apparatus. Sealing can be effected asa single step wherein a stack of alternately positioned membranes andspacers are subjected to radiant energy which effects heating ofselected layers thereby to effect the desired sealing. Alternatively,sealing can be effected of a single set of a membrane and a spacersequentially until a desired stack of alternately positioned membranesand spacers is sealed in the desired configuration.

In accordance with this invention, a dead ended or tangential flowfiltration apparatus is provided which includes a plurality ofspaced-apart membranes and a plurality of spacer layers having channelsor openings that promote liquid flow through the apparatus. The NFFfiltration apparatus is provided with at least one feed port and atleast one filtrate port. The tangential flow filtration apparatus isprovided with at least one feed port, at least one filtrate port and atleast one retentate port. Membrane layers and spacer layers arealternated through the vertical height of the filtration apparatus inselected patterns. Selective sealing of the membrane layers and thespacer layers is effected in a two step process. In a first step, a thinlayer of a thermoplastic polymeric composition is molded onto endportions of each membrane layer that can comprise a membrane or acomposite membrane, such as a membrane supported on a screen layer. Thethermoplastic polymer composition is molded in a pattern which effectsdesired fluid flow through the modules. The thus treated membranes andspacer layers are then stacked in a manner to preliminarily form a feedport, a filtrate port and, in the case of a tangential flow module, aretentate port. The final step of indirect heat-sealing of thermoplasticpolymeric composition preliminarily sealed to the membrane layers thenis selectively effected to form fluid flow channels that separate feedand retentate from filtrate within the module. In the case of atangential flow filtration apparatus, liquid flow within the stack isassured by sealing the feed inlet and the retentate outlet from thefiltrate outlet. The outer portion of the filtration apparatus is thenformed by insert molding. Insert molding is accomplished by positioningthe stack within an injection mold and injecting the molten polymericcomposition into the mold to effect sealing in a manner that assures thedesired liquid flow within the final membrane filtration apparatusduring use. The spacer layers that accept filtrate are sealed by theplastic composition from a feed port extending into the stack so thatthe feed must pass through a membrane layer prior to entering a filtratespacer layer. In addition, the spacer layers adjacent to the feed portthat are designated to accept feed remain in liquid communication withthe feed channel. Channels that accept either retentate or filtrate alsoextend into the stack. The channels that accept retentate are sealedfrom the filtrate spacer layers and are in fluid communication with thespacer layers that are also in fluid communication with the feed port.The channels can extend through the membranes or through thermoplastictabs that are sealed to at least a portion of the periphery of themembranes. The port or ports that accept filtrate are sealed from thespacer layers that accept feed or retentate and are in fluidcommunication with the spacer layers that accept filtrate. The stack isalso sealed in a manner so that liquid feed entering the feed spacerlayers must pass through a membrane before entering a filtrate spacerlayer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a modified membrane structure of thisinvention.

FIG. 2 is a side view of an alternative modified membrane structure ofthis invention.

FIG. 3 is a side view of an alternative modified membrane structure ofthis invention.

FIG. 4 illustrates fluid flow through a tangential flow filtrationmodule of this invention.

FIG. 5 illustrates fluid flow through a tangential flow apparatus ofthis invention.

FIG. 6 is a side view of a modified membrane utilized to form thefiltration apparatus of this invention.

FIG. 7 is a side view of two membranes and one spacer layer utilized toform the filtration modules shown in FIG. 8.

FIG. 8 is a side view of filtration modules of this invention.

FIG. 9 is an exploded cross sectional view of filtration and housingelements utilized to form the filtration apparatus of this invention.

FIG. 10 is a cross sectional view illustrating a final position offiltrate elements of this invention prior to a final forming step forthe filtration apparatus.

FIG. 11 is a cross sectional view illustrating the final step in formingfiltration apparatus of this invention.

FIG. 12 is a perspective view in partial cross-section of a filtrationapparatus of this invention.

FIG. 13 is a graph showing the relative extractable levels of a varietyof polymeric compositions.

FIG. 14 a is a side view of a membrane construction useful for making afiltration module of this invention.

FIG. 14 b is a side view of a membrane construction useful for making afiltration module of this invention.

FIG. 14 c is a top view of the membrane construction of FIGS. 14 a and14 b.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention utilizes filtration membrane elements that can beselectively sealed in a stacked configuration to effect separation offiltrate from feed or feed and retentate. The filtration membraneelement comprises a membrane layer having one edge thereof bonded to athermoplastic polymeric composition. Preferably, the bondedthermoplastic polymeric composition has a top surface and a bottomsurface configured so that they converge toward each other and form anend or tip area. The end or tip area is configured so that it absorbsradiant heat energy or a non heat energy such as ultrasonic energy whichis absorbed by the end and converted to heat energy. When exposed tosuch energy, the end or tip preferentially melts prior to the main bodyof the thermoplastic polymeric composition. This feature permits controlof the direction that the molten thermoplastic polymeric compositionflows that, in turn, permits controlling selective areas of a filtrationapparatus to be sealed. Heating also can be effected by contact with aheated element such as a heated rod.

The filtration membrane elements can be sealed one-by-one to each otheror can be sealed to each other in a desired configuration in a one-stepprocess while positioned in a stack of filtration membrane elements ofthis invention.

The filtration membrane elements useful for forming the filtrationmodule of this invention are formed by modifying an end of a filtrationmembrane by sealing a thermoplastic polymeric composition (TPC) to anedge or perimeter of the filtration membrane. The (TPC) surfaces can besealed to adjacent (TPC) surfaces to effect sealing in a manner thateffects sealing of alternatively positioned spacers in a stack ofmembranes alternating with spacers. Sealing is effected so that anygiven membrane is sealed on one edge and open on an opposing edge.Adjacently positioned membranes separated by an open layer such as ascreen are sealed on opposite edges. This arrangement assures that afeed stream entering an open layer in a stack of membranes and passesthrough a membrane prior to being collected as filtrate. By operating inthis manner, mixing of filtrate with either a feed stream or retentatestream is prevented.

Referring to FIG. 1, a modified membrane structure useful for formingthe filtration module of this invention is shown when the membrane is anultrafiltration membrane 10 having a skin 12 and a layer 14 more porousthan the skin 12. The end 16 is bonded to a (TPC) 18 so that themembrane 10 is sealed at the end 16 by the TPC 18. The TPC 18 isconfigured to have a top surface 20 and a bottom surface 22 whichconverge to form tip 24. The tip 24 functions to concentrate energy suchas radiant or ultrasonic energy to effect melting from tip 24 to thebody 26 of the (TPC). However, it is to be understood that the TPC neednot have converging surfaces and for example, have a flat end or acurved end or the like. A TPC having converging surfaces is preferredsince such a surface configuration effectively concentrates radiant orultrasonic energy at the tip of the TPC.

Referring to FIG. 2, the construction of an alternative filtrationcomposite membrane 30 useful for forming the filtration module of thisinvention is shown wherein the membrane includes a low porosity skin 32,a volume 34 having more open pores than skin 32 and a support layer 36being formed from a more open layer such as spun polypropylene fiber.The composite membrane 30 includes a first molding section 38 that ismolded to the bottom surface 40 of composite membrane 30 and a secondmolding section 42 of composite membrane 30. Second molding section 42includes bottom surface 46 and top surface 49 which converge into tiparea 48. Tip surface 48 preferentially melts when exposed to energy suchas radiant heat or ultrasonic energy over the body 44 of the TPC.

Referring to FIG. 3, an alternative membrane useful for forming thefiltration module of this invention is shown wherein a membrane is shownwhich presents difficulty in bonding to the TPC of choice. The compositemembrane 51 includes a skin 55, a porous body 54 and a porous support 56is bonded to the TPC 58. The skin 55 can be difficult to be bonded byvirtue of its composition such as a glycerin filled layer, or its lowporosity. To improve bonding, a porous screen 60 can be positioned onthe top surface of the skin 55 to effect absorption of molten TPC 58,thereby to improve bonding function to skin 52. The tip 64 functions toconcentrate energy as described above to effect selective melting of theTPC 58 selectively fuse it to the TPC on adjacent layer. This selectivefusion blocks fluid flow past tip 64.

Referring to FIG. 4, a filtration module including the manifold isshown. A filtration element 40 is positioned between manifold 47 andmanifold 11. Manifold 47 is provided with feed inlet 15 and filtrateoutlets 17. Manifold 11 is provided with filtrate outlet 21 andretentate outlet 19. One set of filtrate outlet means 28 is provided onthe manifold 11 while a second set of filtrate outlet means 29 isprovided on the manifold 47. The filtrate outlet means 28 and 29 areconnected to filtrate outlets 17 and 21 by filtrate conduit paths 46.The filtration element 40 includes holes 48 which communicate withliquid inlet means 15 and holes 50 which communicate with filtrateoutlet means 28 and 29.

Referring to FIG. 5, the filtration element 40 includes a filtratespacer 59, a filter layer 53, a retentate spacer 60 and a filter layer62 with a second filtrate spacer (not shown) and which can contactconduit paths 46 (FIG. 4). The liquid feed represented by arrow 61passes through holes 48 in layer 62 into spacer 60. A portion of theliquid passes horizontally through spacer 60, as represented by arrow 64and vertically through filter 53 as represented by arrow 66. Theremaining portion of the incoming liquid passes upwardly as representedby arrow 68, through holes 48 in filter layer 53, holes 48 in filtratespacer 59 and into the next adjacent filtration member (not shown)wherein it proceeds as described above with reference to filtrationelement 40. The filtrate passes into holes 50 and passes in a directionas shown by arrows 70 and 72 toward filtrate outlet means 21 (FIG. 4).Hole 48 alternates with holes 50. The retentate passes across retentatespacer 60 as represented by arrow 64, through holes 50 and to retentateoutlet means 19 (FIG. 4).

Referring to FIG. 6, a membrane layer of the filtration construction ofthis invention is formed from membrane elements 80, 82 and 84 which arespaced apart to form a feed port 86 and a permeate port 88. The element80 is formed from membrane layer 90, a TPC 92, a spacer layer 94, athermoplastic seal section 96 and a thermoplastic seal section 98.Membrane element 82 is formed from membrane layer 107, thermoplasticseal section 98, spacer layer 100, thermoplastic seal section 102 andthermoplastic seal section 104. Membrane element 84 is formed frommembrane layer 106, thermoplastic seal section 108 and thermoplasticseal section 110.

Referring to FIG. 7, a spacer layer is positioned between two membraneelements 80. A spacer layer 114 is positioned between two membraneelements 82. A spacer layer 116 is positioned between two membraneelements 84.

Referring to FIG. 8, thermoplastic seal sections 98 are joined togetherwith a thermoplastic seal 118. Thermoplastic seal sections 104 arejoined together with thermoplastic seal 120. Thermoplastic seal sections108 are joined together with thermoplastic seal 122. Thermoplastic sealsections 110 are joined together with thermoplastic seal 124.

Sealing to the construction of this invention will be described withreference to FIGS. 9, 10 and 11. A stack of the membrane and spacerelements shown in FIG. 8 are vertically positioned with spacers 130interposed between them. Thermoplastic endplates 132, 134 and 136 areformed from a thermoplastic material and a resilient thermoplasticelastomer 140. The resilient thermoplastic elastomer 140 is adapted tobe sealed such as by heat sealing or ultrasonic bonding to thethermoplastic end plates 132, 134 and 136. In addition, resilientthermoplastic elastomer 140 is positioned to cooperate with a pressureplate (not shown) to exert pressure through the vertical height of thefiltration construction of this invention.

As shown in FIG. 10, the periphery of the stack of membranes and spacersis sealed together with a thermoplastic outer housing 142 by casting orinjection molding. In a final step, adjacently positioned thermoplasticconstructions 92 and 98 (FIG. 8) are sealed together with radiant seal144. Sealing means 144 can comprise a radiant seal, an ultrasonic sealor direct contact. Sealing means 144 is positioned sufficiently far fromspacers 146 and 148 so as to prevent sealing of openings 150 and 152 sothat fluid communication can be effected between conduit 86, spacers 148and spacers 152. In addition, filtrate conduit 88 is in selectivecommunication with spacers 154 and 156. In this manner, mixing of feedand retentate filtrate is prevented.

Referring to FIG. 12, the filtration apparatus 160 having inlets 162 and164 for fluid feed, outlets 166 and 168 for retentate and outlets 170and 172 for permeate. In FIG. 12, like designed cross-sections refer tothe same element. The filtration apparatus 160 includes an outer shell174, a sealing elastomer 176, a feed screen 178, a permeate screen 180and a membrane 182.

Referring to FIGS. 13 a, 13 b and 13 c, an alternative set of filtrationelements is shown which can be utilized to form the filtration module ofthis invention. The filtration elements 190 and 192 are stackedvertically one upon the other in alternative layers. Each filtrationelement 190 and 192 includes two membranes 194 and 196, a porous screen198 and two TPC tabs 200 and 202 or 204 and 206. The filtration element190 includes two TPC tabs 207 which are fused to each other when aheating element (not shown) is extended through the port 208. Theheating element is controlled to selectively melt tabs 207 causing themto fuse together. Filtration element 192 is free of tabs 207 and fusionof TPC is not effected by the heating element. Thus, in a stack ofalternating filtration elements 190 and 192 alternating passageways fora liquid to pass into a filtration element 192 are provided. Thefiltration element 192 is provided with TPC tabs on an open end to thatshown which the opposing end of filtration element 190 is free of theTPC tabs. Thus, the opposing ends (not shown) of the filtration elements192 are blocked while the opposing end of filtration element 190 areopen to communication with another port (not shown).

It is to be understood that the membrane layers can be replaced by fluidimpermeable layers having spacer layers alternating with it fluidimpermeable layers. The fluid impermeable layers can be selectivelysealed together in the manner described above so that selective fluidpathways through selected space layers are provided to direct fluid to adesired port which directs fluid into or from the fluid processingmodule such as a fluid manifold or the like.

1. The process for forming a fluid processing module having a feed port,and at least one permeate port that comprises: forming at least onefluid permeable spacer layer having a feed port and at least twomembrane filter layers each having a permeate port wherein said at leastone spacer layer is positioned alternately with said at least two filterlayers in vertical direction, providing at least one thermoplasticsection secured to one end of said two filter layers extending into saidports in a configuration such that when said at least one thermoplasticsection is melted, sealing of said at least two filter layers in saidfeed port is effected such that liquid in said at least one permeateport is not admixed with liquid in said feed port, and heat sealing saidat least one thermoplastic section in one of said ports by extending aradiant heating element in said port and energizing said heating elementto effect heating of said at least one thermoplastic section in saidport to effect heating of all the thermoplastic sections in said portsimultaneously.
 2. The process of claim 1 wherein said heating by theradiant heating element is in the feed port.
 3. The process of claim 1wherein said at least one spacer layer are at least two in number andsaid heating is effected by extending a radiant heating element in oneof said ports and energizing said heating element to effect heating ofall said thermoplastic sections in said port simultaneously.
 4. Theprocess of claim 1 wherein said at least one spacer layer is a pluralityof spacer layers and said at least two filter layers are a plurality offilter layers and said spacer layers and filter layer are arranged inalternate layers and said heating is effected by extending a radiantheating element in at least one of said ports and energizing saidheating element to effect heating of all of said thermoplastic sectionsin said port.
 5. The process of claim 1 wherein said at least one spacerlayer is a plurality of spacer layers and said at least two filterlayers are a plurality of filter layers and said spacer layers andfilter layers are arranged in alternate layers and said heating iseffected by extending a plurality of radiant heating elements in saidports and energizing said heating element to effect heating of all ofsaid thermoplastic sections in said ports simultaneously.
 6. The processof claim 1 wherein said heating by the radiant heating element is in thepermeate port.
 7. The process of claim 1 wherein said heating by theradiant heating element is in the feed port and then the permeate port.8. The process of claim 1 wherein said heating by the radiant heatingelement is in the permeate port and then the feed port.
 9. The processof claim 1 wherein said heating by the radiant heating element is in theretentate port, then the permeate port and then the feed port.
 10. Theprocess of claim 1 wherein said heating by the radiant heating elementis in the retentate port, then the feed port and then the permeate port.11. The process of claim 1 further comprising a retentate port andfurther comprising the step of providing at least one thermoplasticsection secured to each of said two or more filter layers extending intosaid retentate port in a configuration such that when said at least onethermoplastic section is melted, sealing of said at least two filterlayers in said retentate port is effected such that liquid in said atleast one permeate port is not admixed with liquid in said retentate orfeed port.
 12. The process for forming a fluid processing modulecomprising at least one feed port, and at least one permeate port,forming at least two permeable spacer layers, each having a feed portand at least one membrane filter layer having a retentate port whereinsaid at least two spacer layers are positioned alternatively with saidat least one filter layer in a vertical direction, providing at leastone thermoplastic section secured to said at least two spacer layers toat least one end of said spacer layers extending into said ports in aconfiguration such that when said at least one section is melted,sealing of said at least two spacer layers in said at least one permeateport is effected such that liquid in said at least one permeate port isnot admixed with liquid in said feed port, and heat sealing said atleast one thermoplastic section in said ports by extending a radiantheating element in said ports and energizing said heating element toeffect heating of said at least one thermoplastic section in said portsto effect heating of all of the thermoplastic sections in said portsimultaneously.
 13. The process of claim 1 wherein said at least onefilter layer are at least two in number and said heating is effected byextending a radiant heating element in one of said ports and energizingsaid heating element to effect heating of said thermoplasticsimultaneously.
 14. The process of claim 1 wherein said at least twospacer layers are a plurality of spacer layers and said at least onefilter layer is a plurality of filter layers and said spacer layers andfilter layers are arranged in alternate layers and said heating iseffected by extending a radiant heating element in at least one of saidports and energizing said heating element to effect heating of all ofsaid thermoplastic sections in said port.
 15. The process of claim 1further comprising a retentate port and wherein said at least two spacerlayers are a plurality of spacer layers and said at least one filterlayer is a plurality of filter layers and said spacer layers filterlayers are arranged in alternate layers and said heating is effected byextending a radiant heating element in at least one of said ports andenergizing said heating element to effect heating of all of saidthermoplastic sections in said port.
 16. The process of claim 1 whereinsaid at least two spacer layers are a plurality of spacer layers andsaid at least one filter layer is a plurality of filter layers and saidspacer layers and filter layers are arranged in alternate layers andsaid heating is effected by extending a plurality of radiant heatingelements in said ports and energizing said heating element to effectheating of all of said thermoplastic sections in said portssimultaneously.
 17. The process for forming a fluid processing modulecomprising at least one feed port and at least one permeate port,forming at least two fluid permeable spacer layers having a feed portand at least one membrane filter layer having a permeate port, whereinsaid at least two spacer layers are positioned alternately with said atleast one filter layer in a vertical direction, providing at least onethermoplastic section secured to at least one end of said spacer layersextending into a permeate port in a configuration such that when said atleast one section is melted, sealing of said spacer layers in saidpermeate port is effected such that liquid in said permeate port is notadmixed with liquid in a feed port, providing at least one thermoplasticsection secured to at least one end of said at least one filter layerextending into a feed port in a configuration such that when said atleast one section is melted, sealing of said filter layers in said feedport is effected such that liquid in said feed port is not admixed withliquid in said permeate port, and heat sealing said at least onethermoplastic section in said ports by extending a radiant heatingelement in said ports and energizing said heating element to effectheating of said at least one thermoplastic section in said ports toeffect heating of all of the thermoplastic sections in said portsimultaneously.
 18. The process for forming a fluid processing modulecomprising at least one feed port, at least one retentate port and atleast one permeate port, forming at least one fluid permeable spacerlayers having a feed port and at least two membrane filter layer havinga permeate port wherein said at least one spacer layer is positionedalternately with said at least two filter layers in a verticaldirection, providing a thermoplastic section secured to an end of eachof said at least two filter layers extending into the feed port in aconfiguration such that when said thermoplastic sections are melted,sealing of said filter layers in said feed port is effected such thatliquid in said feed port is not admixed with liquid in a permeate port,providing a thermoplastic section secured to an end of each said atleast two filter layers extending into a retentate port in aconfiguration such that when said thermoplastic sections are melted,sealing of said filter layers in said retentate port is effected suchthat liquid in said retentate port is not admixed with liquid in saidpermeate port, and heat sealing said at least one thermoplastic sectionin said ports by extending a radiant heating element in said ports andenergizing said heating element to effect heating of said thermoplasticsections in said ports to effect heating of all of the thermoplasticsection in said port simultaneously.